If the low-energy electron-event excess found in the XENON1T
experiment [1]} does arise from a neutrino magnetic moment,
and the neutrino is a Dirac particle, its diagonal moment could make a substantial contribution
to the inferred effective moment \(\mu _{1T}\) .
A diagonal Dirac moment of this order would, from Eqs. (REF )
and (REF ), lead to a significant spin rotation.
The “naturalness" upper bound to the magnetic moment
of a Dirac neutrino on the
order of \(10^{-14}\mu _B\)   [2]}, would still allow a spin rotation in the range
of detectability. On the other hand, if the neutrino is a Majorana particle, the excess would occur entirely
from transition magnetic moments, with no helicity changes from magnetic fields.
